The optical fiber connector
The fiber optic connector consists of a fiber and a plug at both ends of the fiber. The plug consists of a pin and a peripheral locking structure.According to different locking mechanisms, fiber connectors can be classified into FC type, SC type, LC type, ST type and KTRJ type.
The FC connector adopts a thread locking mechanism and is an optical fiber movable connector which is the earliest and most used invention.
SC is a rectangular joint developed by NTT. It can be directly inserted and removed without thread connection. Compared with FC connector, it has small operation space and is easy to use. Low-end Ethernet products are very common.
The ST connector was developed by AT&T and uses a bayonet locking mechanism.The main parameter indicators are equivalent to FC and SC connectors, but they are not common in company applications. They are usually used in multi-mode devices and are used more often when docked with other manufacturers’ equipment.
KTRJ’s pins are made of plastic and are positioned by steel pins. As the number of insertions and removals increases, the mating surfaces wear and wear, and the long-term stability is not as good as the ceramic pin connectors.
Knowledge of optical fiber
An optical fiber is a conductor that transmits light waves.Optical fiber can be divided into single mode fiber and multimode fiber from the mode of optical transmission.
In single-mode fiber, light transmission has only one fundamental mode, which means that light is transmitted only along the inner core of the fiber.Since the mode dispersion is completely avoided, the single-mode fiber has a wide transmission band and is suitable for high-speed, long-distance fiber communication.
In multimode fiber, there are multiple modes of optical transmission. Due to dispersion or aberration, the transmission performance of such an optical fiber is poor, the frequency band is narrow, the transmission rate is small, and the distance is short.
Optical fiber characteristic parameters
The structure of the optical fiber is prefabricated by a quartz fiber rod, and the outer diameter of the multimode fiber and the single mode fiber for communication are both 125 μm.
The slimming is divided into two areas: the Core and the Cladding layer.The single-mode fiber core has a core diameter of 8~10μm. The multimode fiber core diameter has two standard specifications, and the core diameter is 62.5μm (US standard) and 50μm (European standard).
The interface fiber specification has such a description: 62.5 μm / 125 μm multimode fiber, of which 62.5 μm refers to the core diameter of the fiber, and 125 μm refers to the outer diameter of the fiber.
Single mode fibers use a wavelength of 1310 nm or 1550 nm.
Multimode fibers use a wavelength of 850 nm.
Single mode fiber and multimode fiber can be distinguished in color. The single-mode fiber outer body is yellow, and the multimode fiber outer body is orange-red.
Gigabit optical port
Gigabit optical ports can work in both forced and auto-negotiated modes.In the 802.3 specification, the Gigabit optical port supports only 1000M speed and supports full-duplex (Full) and half-duplex (Half) duplex modes.
The most fundamental difference between auto-negotiation and coercion is that the code stream sent when the two establish a physical link is different. The auto-negotiation mode sends the /C/ code, which is the configuration code stream, and the forced mode sends / I / code, which is the idle stream.
Gigabit optical port self – negotiation process
First: both ends are set to auto-negotiation mode
The two parties send each other/C/code stream. If three identical /C/codes are received consecutively and the received code stream matches the working mode of the local end, the other party returns a /C/ code with an Ack response. After receiving the Ack information, the peer considers that the two can communicate with each other and set the port to the UP state.
Second:one end is set to auto-negotiation, one end is set to mandatory
The auto-negotiation end sends a /C/stream, and the forced end sends the /I/stream. The forcing end cannot provide the peer with the negotiation information of the local end, and cannot return the Ack response to the peer. Therefore, the auto-negotiation terminal DOWN.However, the forcing end itself can recognize the /C/code, and consider that the peer end is a port that matches itself, so directly set the local port to the UP state.
Third:both ends are set to mandatory mode
The two parties send each other/I/streams. After receiving the /I/stream, the peer considers that the peer is the port that matches the peer.
What is the difference between multimode and singlemode fiber?
Multimode:
Fibers that can travel from hundreds to thousands of modes are called multimode (MM) fibers.According to the radial distribution of the refractive index in the core and the cladding, it can be further divided into step multimode fiber and gradual multimode fiber.Almost all multimode fibers are 50/125 μm or 62.5/125 μm in size, and the bandwidth (the amount of information transmitted by the fiber) is usually 200 MHz to 2 GHz.Multimode optical transceivers can carry up to 5 kilometers of transmission over multimode fiber. A light emitting diode or a laser is used as a light source.
Single mode:
A fiber that can only propagate one mode is called a single mode fiber.The standard single mode (SM) fiber refractive index profile is similar to the step fiber, except that the core diameter is much smaller than the multimode fiber.
The size of the single mode fiber is 9-10/125 μm and has an infinite bandwidth and lower loss characteristics than the multimode fiber.Single-mode optical transceivers are often used for long-distance transmission, sometimes reaching 150 to 200 kilometers. LEDs with narrower LD or spectral lines are used as the light source.
Differences and connections:
Single-mode devices typically operate on both single-mode fibers and multimode fibers, while multimode devices are limited to operation on multimode fibers.